The overall objectives of my proposal are to understand the molecular mechanisms by which glutamate receptors, particularly NMDA receptors (NMDARs), interact with synaptic scaffolding proteins and how these interactions shape synaptic transmission. Specifically, I will study how the postsynaptic density-95-like membrane associated guanylate kinase (PSD-MAGUK) protein family, in particular the protein SAP97, traffic NMDA receptors subunits and change their physiology. PSD-MAGUKs and NMDA receptors play a critical role in basal synaptic transmission and learning and memory, and have been implicated in a wide variety of neurological diseases, ranging from developmental disorders such as autism, schizophrenia, to degenerative diseases such as Alzheimer's. My research goals are outlined in two Specific Aims: Specific Aim 1: SAP97 controls AMPA and NMDA receptor trafficking and synaptic morphology. I hypothesize that SAP97 traffics AMPA and NMDARs to synapses during early development and specifically promotes GluN2A-containing NMDARs. Second, I hypothesize that SAP97-mediated signaling also controls dendrite and synapse morphology in developing neurons. I will manipulate SAP97 protein levels in vivo and use electrophysiology and confocal imaging to measure the role of this protein in synaptic transmission and neuronal anatomy. Specific Aim 2: Molecular differences in PSD-MAGUKs underlie NMDAR kinetics and subunit switching. First, I hypothesize that specific protein binding domains shared by PSD-93, -95, and SAP97 promote synaptic trafficking of GluN2A-containing NMDARs while different motifs in SAP102 promote GluN2B- containing receptors. Second, I hypothesize that PSD-MAGUKs also directly influence NMDAR physiology, with each PSD-MAGUK differentially interacting with NMDARs and shaping synaptic currents. I will design and overexpress chimeric PSD-MAGUK proteins in vivo, in NMDAR subunit conditional knockout mice, and measure the effect on NMDARs using electrophysiology. I will also use a heterologous expression system to measure direct interactions between these proteins. Thus, I will define the protein domains responsible for PSD-MAGUK/NMDAR interactions and how these interactions alter NMDAR physiology. These experiments take a multi-dimensional approach to a vital scientific question, combining cutting edge molecular genetic, physiologocial, and anatomical techniques and will enhance our understanding of fundamental molecular mechanisms of synaptic transmission and learning and memory.